As conventional methods for tightening and securing bolts, nuts, or other members, in positions where they are to be located, and also for loosening and removing such members already tightened and secured, there have been known a method in which the power fed from a motor is transferred to a rotatable tightening portion through means of an impact clutch mechanism, and a method in which the power fed from a motor is transferred to a rotatable tightening portion through means of a gear mechanism and a ratchet mechanism.
In the former method of transferring the power from a motor to a rotatable tightening portion through means of an impact clutch mechanism, a relatively large torque is obtained without imparting a reaction to the operator's hand and safe operation can be attained. However, the level of torque is constant, the application of a greater torque causes the clutch to turn OFF, and thus it is impossible to obtain a torque greater than a preset value. In a tightening operation, therefore, after a bolt, a nut, or any other member was tightened with a predetermined torque at a position at which the member is to be located, it is impossible to effect additional tightening by means of the impact device. Conversely, in performance of a loosening operation, it is impossible to first loosen and remove by means of the impact device the above member once the member is strongly tightened with an amount of torque exceeding the torque capacity of the device.
In the latter method of transferring the power from a motor to a rotatable tightening portion through means of a gear mechanism and a ratchet mechanism, a bolt, a nut, or any other member which has been secured by additional tightening or by strongly tightening the member with an amount of torque which is in excess of the torque capacity of the device, can be initially loosened and removed by means of the operator's force. However, if the device is rotatably operated at a torque level which exceeds the tightened torque, the device itself will rotate, so that the operator's hand which holds the device is suddenly moved in the rotating direction, thus often resulting in injury.